Magnetic-kinematic precision stages

ABSTRACT

The application deals with a magnetic-kinematic precision stage system. The essence is, that stages with linear or angular movement are composed of at least two plates, which move with respect to each others on ball joints. The two plates are held together with retaining magnets. This solution garanties the complete elimination of the backlash. The plates may move very freely, practically without force, with respect to each other. Because practically there is no force, as consequent there is very low friction, and thus adjustement with the greatest precision is possible.

ilnited States Patent 1191 Eardocz M IMarch 13, 1973 15 1MAGNETlC-KINEMATHC PRECISION 3,611,577 10/1911 $111111 ..310 111 xSTAGES 3,608,409 9/1971 Schmidt ..310 s.7 x 3,941,331 4/1969 Kesling..248/206 A X [76] lnventor: Arpad Bardocz, Rumannstrasse 57, 2,731,8791/1956 conorerm 248/206AX 8 Munich 23, Germany [22] Filed: June 7, 1971Primary Examiner-J. V. Truhe Assistant Examiner-B. A. Reynolds [211 App!150372 Attorney-Edwin Greigg [30] Foreign Application Priority Data [57]ABSTRACT June 16, 1970 Germany ..P 20 29 715.8 The application dealswith a magnetic-kinematic precision stage system. The essence is, thatstages with [52] 11.8. C1 ..310/8, 248/206 A, 3 10/83 linear or angularmovement are composed of at least [51] Int. Cl. ..H0lv 7/00 two plates,which move with respect to each others on 1 Field of Search ball joints.The two plates are held together with 335/29 243/206 retaining magnets.This solution garanties the 21 1 complete elimination of the backlash.The plates may move very freely, practically without force, with 1References C'ted respect to each other. Because practically there is noUNITED STATES PATENTS force, as consequent there is very low f nctron,and

thus ad ustement with the greatest precision IS possi- 2,850,943 9/1958Grineff ..248/206 A X ble. 2,568,575 9/1951 Wickman ..335/285 X2,952,185 9/1960 Palmer et aL... ..248/206 A X 10 Claims, 15 DrawingFigures PATENIEDMARI 31915 sum 2 0F 3 Fig.3a

MAGNETIC-KINEMATIC PRECIISION STAGES The magnetic-kinematic precisionstages of this invention permit linear and angular motions with aprecision hardly possible in previously-existing devices. In addition totheir application in microscopy, semiconductor technology, and otherbranches of industry, such stages have a special significance in thefields of modern optics, laser technology, holography, and interferometry, to name just a few examples. These technologies requiremechanical stages adjustable with a precision and reproducibility thathas been previously seldom required.

The systems described here are based on completely new constructionprinciples, and permit a greater precision of motion along or around thex, y, and z axes. The basic system is comprised of two plates whichrotate or move laterally with respect to each other on ball joints, andwhich are held together by retaining magnets.

This solution guaranties that all motions are without backlash. Sincethe magnetic force offers no resistance to a motion perpendicular to theforce direction, the plates may move very freely with respect to eachother, and thus may be adjusted with the greatest precision. Theadjustments are made with either ordinary screws or micrometer screws,which are bound to a rigid base. The screw spindle works against amovable part which is held to the spindle by a retaining magnet. Thescrew or micrometer head can be replaced by a piezoelectric coupling.

The significance of this invention may be best appreciated byconsidering the requirements demanded of similar devices and the extentto which this invention satisfies these requirements.

In any precision adjustment which requires an exactness of 0.001 mm orbetter, there are three construction problems which affect thereproducibility of the adjustment. They are: l) backlash between thecomponents; (2) backlash in the adjustment control; and (3) securing auniform motion.

Freedom from backlash: With present-day technology, a device whosefreedom from backlash makes possible a reproducibility on the order of0.00l mm can be achieved only by using a spring action. The springaction can be achieved either by the use of springs or by a springconstruction in the contact guides. Both solutions make the motion moredifficult, since such slides can be moved only by applying a force.

Backlash: ln every mechanical stage, it is necessary to have a retainingforce tending to hold the slide in its original position. In order toeliminate backlash, all present-day stages use springs to provide theretaining force. The use of springs, however, means the application offorce, and indeed, the force changes over the pathlength of the slide.

Uniform motion: Experience shows that a uniform motion re, a jerk-freemotion can be achieved only when the motion is force-free and withoutfriction. Wherever a force is applied, there is also friction, and thusa non-uniform motion. It is clear that it is ad vantageous for themotion to result from the smallest possible forces. With present-daytechnology, this is the case for the magnetic-kinematic solution of thisinvention.

It should be explicitly stated that piezoelectric ceramic materials havegreat significance in achieving motions of the highest fineness.Piezoelectric transducers are by their nature not suitable fortransmitting large forces. Thus the magnetic-kinematic devices of thisinvention are extremely well suited for operation with piezoelectrictransducers.

The invention will be better understood, and further objects andadvantages will become more apparent, from a reading of the followingspecification taken in conjunction with the drawing, wherein:

FIG. la is a front elevation of one embodiment of the invention;

FIG. 1b is a plan view of FIG. 1a;

FIG. 2a is a front elevation of a second embodiment of the invention;

FIG. 2b is a plan view of FIG. 2a;

FIG. 3a is a front elevation of another embodiment;

FIG. 3b is a plan view of FIG. 3a;

FIG. 4 is an exploded perspective view of elements shown in FIGS. 3a and3b;

FIG. 5 is a schematic plan view showing one position of the micrometerscrew for adjustment on the x-axis;

FIG. 6 is a schematic plan view of another position of said micrometerscrew;

FIG. 7 is a schematic plan view of another position of said micrometerscrew;

FIG. 8a is a front elevation of another embodiment of the invention;

FIG. 8b is a side elevation of FIG. 8a;

FIG. 8c is a schematic view showing the various adjustments which can bemade by the device of FIGS. 8a and 8b;

FIG. 9a is a front elevation of another embodiment of the invention; and

FIG. 9b is a plan view of FIG. 9a.

FIG. (la) and (lb) show a linear translating stage. The two opposingparts of this linear magnetic-kinematic translating stage roll on ballsconfined in linear grooves, the individual parts being held together bymagnetic forces. FIG. (la) and (lb) show the application of amagnetic-kinematic system in an optical device. As shown there, thetwo-piece linearly-translating member (V) and (Z) are mounted onto anoptical bench rider (R). The upper part of the translating member is aslide which rests upon balls and is movable in the plane of the FIG.(lb). The two parts of the translating member are held togethermagnetically as shown by arrows m.a. indicating the magnetic attraction.A Knob (T), covered on the side with plastic, provides a coarseadjustment of the slide. The fine motion is made with a micrometer screw(M). The micrometer screw is attached to the lower part of thetranslating member (V) and holds the slide with a magnet (N). A devicetranslatable in two perpendicular directions (x and y direction) ispossible by combining two of the translating devices shown in FIG. Iaand lb.

Magnetic-kinematic movements are also very well suited for producingangular rotations. FIG. 2a and 2b show a device in which a precisionadjustment around the z-axis (the vertical axis) is possible. Theexample is taken from an optical device. The rider column (S) isfastened to a disc (U) which rotates with respect to a lower part (R).The disc rests upon balls confined in matching circular grooves milledinto the two parts, and the parts are held together magnetically asindicated by arrows m.a. The lower part rests upon an optical benchrider (R) and may be fastened to it with magnets. The disc, and hencealso the column, may be rotated through a full 360. The micrometer screw(M) acts against a protrusion (G) from the rotating disc and is fastenedto it by a coupling magnet. The protrusion may be set at any desiredposition along the edge of the disc.

If a circular groove is milled onto the optical rider (R), the rotatingdisc may be set directly on the optical rider.

The x and y translation and the rotation about the z axis, as shown inFIGS. 11: and lb, and 2a and 2b, can be built together into a singleunit, as shown in FIG. 3a and 3b. For better understanding, this figureis shown in an exploded view in FIG. 4.

The placement of adjustment screws or micrometer heads in themagnetic-kinematic system represents a special problem. Basically, it isoften necessary to restrict the dimension of the device along thedirection of the motion (x-axis). The problem does not generally occurin the y-direction. When the problem occurs, the micrometer head shouldbe placed either over or next to the slide. FIGS. 5, 6, and 7 showvarious possibilities for locating the adjustment device on thex-direction slide.

FIG. 5 shows a device in which the adjustment screw or micrometer headis located as an extension of the slide.

FIG. 6 shows a device in which the adjustment screw or micrometer headis located on top of the slide.

FIG. 7 shows a device in which the adjustment screw or micrometer headis located to the side of the slide.

Magnetic-kinematic adjustments are especially significant for precisionvertical motions. Vertical adjustments in precision translating devicespresent an especially difficult problem. The difficulty lies inbalancing out the weight of the object being supported. The principle ofthis invention solves this problem also, in that it completely removesthe effect of the weight.

FIG. 8a, 8b and 8c show the elegant and complete solution for theprecision vertical translating stage. The device is coupled with doublelinear translation motions in the vertical plane, and the entire deviceis mounted on an optical bench rider (R). The component' to be moved inthe vertical direction for example, a lens or mirror (0) hangs from acolumn (P1). The column has straight guide grooves on both sides,corresponding on one side to guide grooves in the mirror holder (0) andon the other side to guide grooves in a counterweight (P3). The mirrorholder and counterweight are suspended from the ends of a metal band(Ml), which hangs over a ball-bearing roller (K) mounted at the top ofthe column. The mirror can be rotated a full 360 about either the y(horizontal) axis or the z (vertical) axis. The rotational action aboutthe y (horizontal) and z (vertical) axis is made with the help ofmagnetic-kinematic rotation stages (U P2) and (V) the magneticattraction between these stages being indicated by arrows m.a. Forclarity, the adjusting screws or micrometer heads are not shown in thefigure. The coarse vertical adjustment of the optical component is to bemade by hand, and the fine adjustment by an ordinary screw or by amicrometer screw. Since the screw must be attached at various heights,it is attached magnetically.

FIG. 9a and 9b show how elegantly the magnetickinematic principle can beapplied to a piezoelectrically-controlled translation. Again, an opticalexample is given. It should be mentioned that in all presently availablepiezoelectric optical mounts, the piezoelectric transducer is rigidlymounted at one of its ends and supports the optical component at theother end. If the transducer is arranged horizontally, this means amechanical load on the transducer column, so that the column has atendency to bend. Such a system becomes complicated when the beam mustpass through the system. In this case the transducer is built as alargediameter ring.

The linear translation stage (T1, T2, M) of FIG. 1 is again shown inFIG. 9a and 9b. One end of the piezoelectric transducer (P) is attachedto the fixed part (T1) of the translation stage. The upper slide (T2)carries a stub (Z1); against which the translating force of thepiezoelectric transducer acts. The end of the piezoelectric transducerwhich pushes against the stub is provided with a retaining magnet, inorder to ensure a contact without mechanical backlash. It is seen fromFIG. 9a and 9b that the only mechanical load on the piezoelectric columnis a push or pull along its axis, and that the dimensions of this columnare completely independent of the optical components. The points labeledx and y are the electrical terminals for the voltage across thepiezoelectric transducers.

It is obvious that this principle can also be applied to rotatingstages.

Iclaim:

1. In an apparatus for precision adjustment comprising a first member, asecond member juxtaposed to said first member, antifriction meansseparating said members, magnetic means urging said members towards eachother and means acting between said members to move one member relativeto another, said means being magnetically attached to at least one ofsaid members.

2. An apparatus as claimed in claim 1 in which the means acting betweensaid members comprises a micro-moving means and an end of saidmicromoving means is magnetically attached to said one member.

3. An apparatus as claimed in claim 1 in which there is a base memberand said first member is adjustable with respect to the base member by acoarse adjustment means.

4. An apparatus as claimed in claim 2 in which the second member isrotatable with respect to the first member about a vertical axis andsaid end of the micromoving means acts against a radially extendingshoulder on said second member.

5. An apparatus as claimed in claim 2 in which a third member isjuxtaposed to said second member with anti-friction means separatingsaid second and third members and magnetic means urging said second andthird members together, said third member being rotatable with respectto said second member about a vertical axis, and second micromovingmeans acting between said second and third members, an end of saidsecond micromoving means acting against a radially extending shoulder onsaid third member.

6. An apparatus as claimed in claim 5 in which a standard is supportedon said third member, a fourth member is supported for verticaladjustment on said standard and a fifth member is juxtaposed to saidfourth member for rotational movement with respect thereto, said fifthmember being separated from said fourth member by antifriction means andbeing urged towards said fourth member by magnetic means, andmicromoving means acting between said fourth and fifth members.

7. An apparatus as claimed in claim 6 in which said fifth membersupports an optical device for rotation about a vertical axis and saidfourth member, fifth member and optical device are counterbalanced by aweight supported by flexible means.

8. An apparatus as claimed in claim 7 in which said first member isjuxtaposed to a slide member, said first member and slide member beingmagnetically urged towards each other, micromoving means acting betweensaid slide member and said first member to cause relativ'e movementbetween them, said slide member being adapted to be adjustably mountedon a track member, the first, second and third members beinghorizontally positioned plate members vertically stacked on top of saidslide member, the first and second members being adjustable by saidmicromoving means in a direction at right angles to the direction inwhich the micromoving means adjusts the first member with respect to theslide member.

9. An apparatus as claimed in claim 2 in which said micromoving means isa piezoelectric device.

110. An apparatus as claimed in claim 9 in which there is a base membersupporting said first and second members and a micrometer screw actsbetween said base member and said first member to cause relativemovement between them.

1. In an apparatus for precision adjustment comprising a first member, asecond member juxtaposed to said first member, antifriction meansseparating said members, magnetic means urging said members towards eachother and means acting between said members to move one member relativeto another, said means being magnetically attached to at least one ofsaid members.
 1. In an apparatus for precision adjustment comprising afirst member, a second member juxtaposed to said first member,antifriction means separating said members, magnetic means urging saidmembers towards each other and means acting between said members to moveone member relative to another, said means being magnetically attachedto at least one of said members.
 2. An apparatus as claimed in claim 1in which the means acting between said members comprises a micro-movingmeans and an end of said micromoving means is magnetically attached tosaid one member.
 3. An apparatus as claimed in claim 1 in which there isa base member and said first member is adjustable with respect to thebase member by a coarse adjustment means.
 4. An apparatus as claimed inclaim 2 in which the second member is rotatable with respect to thefirst member about a vertical axis and said end of the micromoving meansacts against a radially extending shoulder on said second member.
 5. Anapparatus as claimed in claim 2 in which a third member is juxtaposed tosaid second member with anti-friction means separating said second andthird members and magnetic means urging said second and third memberstogether, said third member being rotatable with respect to said secondmember about a vertical axis, and second micromoving means actingbetween said second and third members, an end of said second micromovingmeans acting against a radially extending shoulder on said third member.6. An apparatus as claimed in claim 5 in which a standard is supportedon said third member, a fourth member is supported for verticaladjustment on said standard and a fifth member is juxtaposed to saidfourth member for rotational movement with respect thereto, said fifthmember being separated from said fourth member by antifriction means andbeing urged towards said fourth member by magnetic means, andmicromoving means acting between said fourth and fifth members.
 7. Anapparatus as claimed in claim 6 in which said fifth member supports anoptical device for rotation about a vertical axis and said fourthmember, fifth member and optical device are counterbalanced by a weightsupported by flexible means.
 8. An apparatus as claimed in claim 7 inwhich said first member is juxtaposed to a slide member, said firstmember and slide member being magnetically urged towards each other,micromoving means acting between said slide member and said first memberto cause relative movement between them, said slide member being adaptedto be adjustably mounted on a track member, the first, second and thirdmembers being horizontally positioned plate members vertically stackedon top of said slide member, the first and second members beingadjustable by said micromoving means in a direction at right angles tothe direction in which the micromoving means adjusts the first memberwith respect to the slide member.
 9. An apparatus as claimed in claim 2in which said micromoving means is a piezOelectric device.